Partial nitritation at elevated loading rates: design curves and biofilm characteristics.

There is a need to develop low operational intensity, cost-effective, and small-footprint systems to treat wastewater. Partial nitritation has been studied using a variety of control strategies, however, a gap in passive operation is evident. This research investigates the use of elevated loading rates as a strategy for achieving low operational intensity partial nitritation in a moving bed biofilm reactor (MBBR) system. The effects of loading rates on nitrification kinetics and biofilm characteristics were determined at elevated, steady dissolved oxygen concentrations between 5.5 and 7.0 mg O2/L and ambient temperatures between 19 and 21 °C. Four elevated loading rates (3, 4, 5 and 6.5 g NH4+-N/m2 days) were tested with a distinct shift in kinetics being observed towards nitritation at elevated loadings. Complete partial nitritation (100% nitrite production) was achieved at 6.5 g NH4+-N/m2 days, likely due to thick biofilm (572 µm) and elevated NH4+-N load, which resulted in suppression of nitrite oxidation.

Investigation of copper inhibition of nitrifying moving bed biofilm (MBBR) reactors during long term operations.

Copper, a prevalent heavy metal in industrial mining wastewaters, has been shown to inhibit nitrification in wastewater treatment systems. Biofilm treatment systems have an inherent potential to reduce inhibition. This study investigated the effects of copper concentration on nitrifying biofilms in moving bed biofilm reactor (MBBR) systems across long term operation using influent ammonia concentrations representative of gold mining wastewater. Conventional isotherm models did not adequately model the attachment of copper to the biofilm. Long term nitritation was shown to be uninhibited at influent copper concentrations between 0.13 and 0.61 mg Cu/L. Nitratation was inhibited with influent copper concentrations of 0.28-0.61 mg Cu/L. There was no statistical difference in biofilm characteristics, including biofilm thickness, mass and density, across all copper concentrations tested, however, changes in biofilm morphology were observed. The demonstrated resistance of the nitrifying biofilm to copper inhibition makes the MBBR system a promising technology for treating ammonia in mining wastewaters.

Halotolerance and effect of salt on hydrophobicity in hydrocarbon-degrading bacteria.

Hydrocarbon-contaminated environments often also experience co-contamination with elevated levels of salt. This paper investigates the occurrence of halotolerance among several hydrocarbon-degrading bacteria, as an initial assessment of the importance of salt contamination to bioremediation strategies. Halotolerance was common, but not ubiquitous, among the 12 hydrocarbon-degrading bacteria tested, with many strains growing at up to 75 or 100 g NaCl L(-1) in rich medium. Greater sensitivity to elevated salt concentrations was observed among aromatics degraders compared to saturates degraders, and in defined medium compared to rich medium. Observed effects of high salt concentrations included increased lag times and decreased maximum growth. Many strains exhibited flocculation at elevated salt concentrations, but this did not correlate to any patterns in cell surface hydrophobicity, measured using the Bacterial Adhesion to Hydrocarbon assay. The occurrence of halotolerance in hydrocarbon-degrading bacteria suggests the potential for native microorganisms to contribute to the bioremediation of oil and salt co-contaminated sites, and indicates the need for a better understanding of the relationship between halotolerance and hydrocarbon biodegradation capabilities.

Electricity generation by Propionibacterium freudenreichii in a mediatorless microbial fuel cell.

OBJECTIVE: To test Propionibacterium freudenreichii as a novel biocatalyst in a glycerol-oxidizing microbial fuel cell (MFC). RESULTS: Two strains, P. freudenreichii ssp. shermanii and P. freudenreichii ssp. freudenreichii, were screened as anodic biocatalysts and shown to produce power from glycerol in an MFC. Voltage was generated with and without resazurin in the medium, showing that both strains are exoelectrogenic. Polarization data showed that an MFC with P. freudenreichii ssp. shermanii reached a maximum open circuit voltage of 485 mV and a maximum power density of 14.9 mW m(-2). Glycerol consumption was about 50 % lower in MFCs than in fermentations, indicating a metabolic shift in the MFC environment. CONCLUSION: P. freudenreichii ssp. shermanii and P. freudenreichii ssp. freudenreichii were shown for the first time to act as exoelectrogenic anodic biocatalysts in MFCs.

Comparison of Escherichia coli and anaerobic consortia derived from compost as anodic biocatalysts in a glycerol-oxidizing microbial fuel cell.

Using glycerol from biodiesel production as a fuel in a microbial fuel cell (MFC) will generate electricity and value-added by-products from what is currently considered waste. This research screened Escherichia coli W3110 (ATCC 27325) and a mixed culture enriched from compost (AR2) as anodic biocatalysts in a mediatorless glycerol-oxidizing MFC. In an H-type MFC, the mixed culture AR2 biocatalyst produced a maximum power density of 11.7mWm(-2) compared to 9.8mWm(-2) using E. coli W3110 as the anodic catalyst. In batch operation of the fuel cell, the mixed culture AR2 was able to anaerobically consume 29g/L of glycerol compared to only 3.3g/L using the E. coli strain. The mixed culture was also shown to concurrently produce 1,3-propanediol, a value-added product, and electricity from a pure glycerol feedstock in an MFC.

Aerobic biotransformation of decalin (decahydronaphthalene) by Rhodococcus spp.

Mixed bacterial cultures aerobically transformed decalin (decahydronaphthalene) dissolved in an immiscible carrier phase (heptamethylnonane; HMN) in liquid medium. Conversion was enhanced in the presence of decane, a readily degraded n-alkane, and/or HMN. Four Rhodococcus spp. isolates purified from one of the mixed cultures were active against decalin in the presence of n-decane, but their ability to use decalin as a sole carbon source for growth could not be sustained. Isolate Iso 1a oxidized decalin under co-metabolic conditions with decane vapours as the primary carbon source. Mass spectrometry and comparison to authentic standards showed that the oxidized products of decalin biotransformation were 2-decahydronaphthol and 2-decalone. Some evidence of ring-opening was obtained, but the possible ring-opened product was not definitively identified. These results are consistent with co-metabolic oxidation of decalin by enzymes active toward n-alkanes.

Sulfur from benzothiophene and alkylbenzothiophenes supports growth of Rhodococcus sp. strain JVH1.

Rhodococcus sp. strain JVH1 was previously reported to use a number of compounds with aliphatic sulfide bridges as sulfur sources for growth. We have shown that although JVH1 does not use the three-ring thiophenic sulfur compound dibenzothiophene, this strain can use the two-ring compound benzothiophene as its sole sulfur source, resulting in growth of the culture and loss of benzothiophene. Addition of inorganic sulfate to the medium reduced the conversion of benzothiophene, indicating that benzothiophene metabolism is repressed by sulfate and that benzothiophene is therefore used specifically as a sulfur source. JVH1 also used all six isomers of methylbenzothiophene and two dimethylbenzothiophene isomers as sulfur sources for growth. Metabolites identified from benzothiophene and some methylbenzothiophenes were consistent with published pathways for benzothiophene biodesulfurization. Products retaining the sulfur atom were sulfones and sultines, the sultines being formed from phenolic sulfinates under acidic extraction conditions. With 2-methylbenzothiophene, the final desulfurized product was 2-methylbenzofuran, formed by dehydration of 3-(o-hydroxyphenyl) propanone under acidic extraction conditions and indicating an oxygenative desulfination reaction. With 3-methylbenzothiophene, the final desulfurized product was 2-isopropenylphenol, indicating a hydrolytic desulfination reaction. JVH1 is the first microorganism reported to use all six isomers of methylbenzothiophene, as well as some dimethylbenzothiophene isomers, as sole sulfur sources. JVH1 therefore possesses broader sulfur extraction abilities than previously reported, including not only sulfidic compounds but also some thiophenic species.

Selectivity among organic sulfur compounds in one- and two-liquid-phase cultures of Rhodococcus sp. strain JVH1.

The selectivity of Rhodococcus sp. strain JVH1 among selected sulfidic and thiophenic compounds was investigated in both single-liquid-phase (aqueous) cultures and in two-liquid-phase cultures, where the sulfur compounds were dissolved in 2,2,4,4,6,8,8-heptamethylnonane as the immiscible organic carrier phase. In the single-liquid-phase cultures, Rhodococcus sp. strain JVH1 showed a preference for benzyl sulfide over both 1,4-dithiane and benzothiophene. An increased lag was observed in the degradation of benzyl sulfone and benzothiophene sulfone when both compounds were present. These results were consistent with a competitive inhibition mechanism, affecting both sulfur oxidation and carbon-sulfur bond cleavage. In the two-liquid-phase cultures, the effect of partitioning between the two liquid phases dominated the desulfurization activity of the culture. This partitioning resulted in an apparent absence of selectivity, as well as decreases in lag time, extent of degradation, and time to completion of degradation. Desulfurization activity also depended on the growth phase of the cultures. Mass transfer rate limitations were not observed at the low degradation rates of 0.02 mmol day(-1) l(-1). Owing to the importance of partitioning, Rhodococcus sp. strain JVH1 is predicted to show nonselective activity towards the sulfur species in a whole crude oil.